(1) FIELD OF THE INVENTION:
This invention relates in general to earth boring drill pipe and to hardsurfacing of tool joints or connection members relative to the drill pipe.
(2) DESCRIPTION OF THE PRIOR ART:
The most common drill pipe used in earth boring operations have connection members or tool joints on each end that are larger in diameter than the drill pipe. Annular bands of hardfacing are commonly deposited on each tool joint. One type of hardfacing has macroscopic sintered tungsten carbide granules within an alloy steel matrix. Sintered tungsten carbide granules, as explained in U.S. Pat. No. 3,800,891, comprise microscopic grains of tungsten carbide held together by a binder of an iron group metal, usually cobalt. Sintered tungsten carbide hardfacing is normally applied on tool joints by rotating the tool joint, providing an arc with a consumable steel wire, discharging an inert gas around the wire, and gravity feeding sintered tungsten carbide granules into the weld puddle behind the wire.
One disadvantage of the resulting sintered tungsten carbide hardfacing is that many of the granules remain only partially embedded in the matrix, giving a rough, abrasive exterior. In deep wells, intermediate strings of casing are set as the well is drilled. While drilling deeper through a string of intermediate casing, the rough surface of the hardfacing can abrade and damage the casing. Consequently, it is advantageous to have a hardfacing surface free of protruding tungsten carbide granules. In U.S. Pat. No. 4,243,727, entitled "Surface Smoothed Tool Joint Hardfacing", a method and apparatus is shown for hardfacing tool joints using tungsten carbide granules that results in a smooth exterior. The granules are dropped directly into the arc, rather than behind the arc. This concentrates the granules toward the bottom of the hardfacing deposit and results in a harder matrix near the bottom, as well.
In U.S. Pat. No. 4,228,339, an improved method for hardsurfacing the tool joints is provided in which annular bands of hardfacing are applied using tungsten carbide granules in a steel matrix applied by means of an electrode to the welding puddle.
It has been discovered that it is extremely difficult to machine down the hardfacing containing the tungsten carbide granules, because of their extreme hardness. The removal of the outer layer of tungsten carbide granules in hardfacing is necessary so that the hardfacing itself will not cut into or wear a surface of the casing through which the tool joint typically will be inserted. In instances in which tungsten carbide granules are within the matrix forming the hardfacing, considerable time is required to machine down the tungsten carbide granules, thus contributing significantly to the total cost of the hardfacing operation. The present invention is an improvement upon the process and product of the '339 patent, cited above, in that the puddle containing the steel matrix and the tungsten carbide granules therein is deposited in the grooves by the electrode to a given depth and thereafter the feed of granules into the weld puddle is discontinued with a continuation of the application of the puddle by the electrode to the groove to provide a protruding substantially tungsten carbide free hardfacing surface above the outer diameter of the tool joint. The protruding substantially tungsten carbide free hardfacing may then be machined down to substantially the outer diameter of the tool joint. Because the protruding hardfacing surface does not contain tungsten carbide granules, the machining operation may be effected with considerable savings of time and equipment.
The present invention provides a method of applying grooved bands of hardfacing on a tool joint for earth boring drill pipe, the hardfacing having tungsten carbide granules in an alloy steel matrix. The method includes the steps of rotating the tool joint, providing an arc between an electrode and the tool joint to create a weld puddle. The electrode is reciprocated parallel to the tool joint axis and granules are fed into the weld puddle. The weld puddle with the granules is applied within the grooved bands around the exterior of the tool joint to a grooved depth of from between about 0.75 inches to about 0.150 inches. Thereafter, the feed of the granules into the weld puddle is discontinued. The weld puddle is continued to be applied around the tool joint and in the grooved bands to provide a protruding substantially tungsten carbide free hardfacing surface above the outer diameter of the tool joint of from between about 0.050 inches to about 0.175 inches. Thereafter, the hardfacing surface is machined down to substantially the outer diameter of the tool joint.